Ammunition cartridge cases serve many purposes by providing the ability to combine a projectile, a primer and a propellant into one complete system. This complete system allows for a cartridge to be placed within a weapon and fired such that the projectile exits a barrel of the weapon at a high rate of speed in an attempt to strike a desired target. During combustion of the cartridge, the cartridge case obturates a chamber of the weapon as a result of pressure exerted thereon by gunpowder combustion gases while providing a finite volume for the controlled ignition of the gunpowder to take place. After firing of the ammunition, the cartridge case has served its purpose and is typically discarded, recycled, or reloaded.
While primer and gunpowder serve critical roles in conveying the projectile toward a desired target, the cartridge packaging does not directly progress the projectile toward the target and as such cartridge modification would minimally affect the overall system performance. Thus, if a lightweight cartridge case could be engineered, such that the system provided the same functionality, but with a lighter weight, an overall system performance increase could be obtained. For example, a soldier or individual could carry additional ammunition at the same basic load or carry an equal amount of ammunition with a reduced weight burden. Similar benefits could be demonstrated on larger mobile platforms, such as aircraft, where weight-limiting factors also exist.
Small caliber ammunition cartridge cases typically consist of brass that has been formed through a series of cold working and annealing steps. This process results in a graded microstructure that produces higher hardness and strength near the base of the cartridge and a graded hardness and strength along the length of the sleeve sidewalls. The base of the cartridge is substantially thicker than the remainder of the cartridge, as it serves to hold the primer in place, as well as allow for extraction of the cartridge case from the weapon after firing. Thus the base area possesses the highest mass of the entire cartridge. Weight savings of the ammunition can be obtained by substituting steel for brass. However, to achieve larger reductions in weight for the ammunition, additional changes are needed. Therefore, an ammunition cartridge case with greater weight savings compared to traditional brass cartridge cases is desired.